A model to study charge transport processes in mesoporous films of dye-sensitized solar cells is presented. By simulating electron and ion transport by Brownian dynamics in these films, a direct relation between grain connectivity and effective diffusion coeffs. was obtained. By comparing the macroscopic properties of a simple cubic and a diamond-structured unit cell, the latter better resembles the properties of the mesoporous oxide films in comparison with exptl. results. The model was used to optimize the size of the contact area between the interconnected particles in the mesoporous film with respect to the photocurrent.